<?xml version="1.0" encoding="UTF-8"?>
     <grammar
       xmlns="http://relaxng.org/ns/structure/1.0"
       xmlns:a="http://relaxng.org/ns/compatibility/annotations/1.0"
       datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes"
       ns="urn:ietf:params:xml:ns:imdn">

         <start>
             <element name="imdn">
                 <element name="message-id">
                     <data type="token"/>
                 </element>
                 <element name="datetime">
                     <data type="string"/>
                 </element>
                 <optional>
                     <element name="recipient-uri">
                         <data type="anyURI"/>
                     </element>
                     <element name="original-recipient-uri">
                         <data type="anyURI"/>
                     </element>
                     <optional>
                         <element name="subject">
                             <data type="string"/>
                         </element>
                     </optional>
                 </optional>
                 <choice>
                     <ref name="deliveryNotification"/>
                     <ref name="displayNotification"/>
                     <ref name="processingNotification"/>
                     <empty/>
                 </choice>
                 <ref name="imdnExtension"/>
             </element>
         </start>

         <define name="deliveryNotification">
             <element name="delivery-notification">
                 <element name="status">
                     <choice>
                         <element name="delivered">
                             <empty/>
                         </element>
                         <element name="failed">
                             <empty/>
                         </element>
                         <ref name="commonDispositionStatus"></ref>
                     </choice>
                     <ref name="deliveryExtension"/>
                   </element>
              </element>
         </define>

         <define name="displayNotification">
             <element name="display-notification">
                 <element name="status">
                     <choice>
                         <element name="displayed">
                             <empty/>
                         </element>
                         <ref name="commonDispositionStatus"></ref>
                     </choice>
                     <ref name="displayExtension"/>
                 </element>
             </element>
         </define>

         <define name="processingNotification">
             <element name="processing-notification">
                 <element name="status">
                     <choice>
                         <element name="processed">
                             <empty/>
                         </element>
                         <element name="stored">
                             <empty/>
                         </element>
                         <ref name="commonDispositionStatus"></ref>
                     </choice>
                     <ref name="processingExtension"/>
                  </element>
             </element>
         </define>

         <define name="commonDispositionStatus">
             <choice>
                 <element name="forbidden">
                     <empty/>
                 </element>
                 <element name="error">
                     <empty/>
                 </element>
             </choice>
         </define>

         <!-- <imdn> extension point for the extension schemas to add
              new definitions with the combine="interleave" pattern.
              Extension schemas should add proper cardinalities. For example, the
              <zeroOrMore> cardinality should be used if the extension is to allow
              multiple elements, and the <optional> cardinality should be used if the
              extension is to allow a single optional element. -->
         <define name="imdnExtension">
             <zeroOrMore>
                 <ref name="anyIMDN"/>
             </zeroOrMore>
         </define>

         <!-- delivery-notification <status> extension point -->
         <define name="deliveryExtension">
             <zeroOrMore>
                 <ref name="anyIMDN"/>
             </zeroOrMore>
         </define>

         <!-- display-notification <status> extension point -->
         <define name="displayExtension">
             <zeroOrMore>
                 <ref name="anyIMDN"/>
             </zeroOrMore>
         </define>

         <!-- processing-notification <status> extension point -->
         <define name="processingExtension">
             <zeroOrMore>
                 <ref name="anyIMDN"/>
             </zeroOrMore>
         </define>

         <!-- wildcard definition for complex elements (of mixed type)
              unqualified or qualified in the imdn namespace.
              Extension schemas MUST redefine this or the
              individual previous definitions which use this definition.
              In other words, the extension schema MUST reduce the
              allowable content in order to maintain deterministic
              and unambiquous schemas with the interleave pattern. -->
         <define name="anyIMDN">
             <element>
                 <anyName>
                     <except>
                         <nsName ns="urn:ietf:params:xml:ns:imdn"/>
                         <nsName ns=""/>
                     </except>
                 </anyName>
                 <ref name="anyExtension"/>
             </element>
         </define>

        <!-- the rest of the "anyIMDN" wildcard definition -->
         <define name="anyExtension">
             <zeroOrMore>
                <choice>
                    <attribute>
                       <anyName/>
                    </attribute>
                    <ref name="any"/>
                </choice>
             </zeroOrMore>
         </define>

         <!-- wildcard type for complex elements (of mixed type)
              without any namespace or content restrictions -->
         <define name="any">
             <element>
                 <anyName/>
                 <zeroOrMore>
                    <choice>
                       <attribute>
                          <anyName/>
                       </attribute>
                       <text/>
                       <ref name="any"/>
                    </choice>
                 </zeroOrMore>
             </element>
         </define>

    </grammar>